Photo-sensitive apparatus



New. 30, 1937. D. D. KNOWLES PHOTOSENSITIVE APPARATUS Original Filed Nov. 19, 1926 Indicfiny De vice INVENTOR I De weyD. Know/es.

WITNESSES:

Patented Nov. 30, 1937 UNITED STATES PATENT Fl PHOTO-SENSITIVE APPARATUS Original application November 19, 1926, Serial No. 149,290. Divided and this application June 21, 1933, Serial No. 676,903

2 Claims.

My invention relates to electric discharge apparatus and it has particular relation to relay systems of the type incorporating electric discharge devices generally known as glow tubes.

The present invention is a division of my application Serial No. 149,290, filed November 19, 1926 and assigned to the Westinghouse Electric & Manufacturing Company now issued as Patent No. 2,062,268. Patent No. 2,062,270 filed June 21,

10.1933, and assigned to Westinghouse Electric &

Manufacturing Company is a division of the present application.

An object of my invention is to provide a relay of the type incorporating a glow tube provided with a self-contained discharge-controlling. ele-' ment.

Another object of my invention is to provide a photo-sensitive relay of the type incorporating a glow tube capable of delivering considerable current and controlled solely by the small output current of a photo-sensitive device.

More concisely stated it is an object of my invention to provide an electric discharge device for greatly amplifying a minute current such as is obtained from an energized photo-cell.

There is, at the present, a large field of usefulness for a potential-controlled relay capable of handling comparatively large currents. Multistage amplifiers, utilizing the usual three-electrode thermionic tubes have been employed in the past, but they are expensive to build and maintain in operation and are not entirely dependable. In addition, the thermionic amplifiers are not entirely satisfactory when an attempt is made to supply anode potential from a source of alternating potential.

I have accordingly designed a gaseous relay having two cold principal electrodes incorporated therein between which the output current passes,

and a third, or control, electrode so arranged as to regulate the passage of the output current. The relay provided in accordance with my invention is dependent for its operation in the Variation of the current transmitted between the principal electrodes for variations in the potentials impressed between the control electrode and the principal electrodes;

fhe novel features which I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description and to the drawing, in which 5 Figure l is a view partly diagrammatic and partly in section showing an embodiment of my invention, and

Fig. 2 is a View Partly diagrammatic and partly in section showing another modification of my 10 invention.

If a potential is applied between an electrode havingra large surface and a point electrode in the presence of an ionizable gas, a discharge will take place. Tubes have been developed for main- 15 taining a constant voltage across the electrodes, regardless of the current flowing within certain limits and areknown commercially as voltageregulator glow-tubes.

It is generally known that the drop in voltage near the cathode of a glow-discharge tube is constant until the current is so large that the glow covers the whole cathode. The constant voltage drop at the cathode is called the cathode fall of potential and depends on thekind of gas used and the electrode material. When the gas is argon or neon and the cathode is made of, or coated with, sodium, potassium, or caesium, this cathode drop will be of the order of volts.'

A tube utilizing but two' electrodes becomes active as soon as a critical voltage is applied. In order to adapt glow tubes of this type for use as relays, it was accordingly necessary to provide means for instantaneously stopping or starting the discharge independently of the applied voltage. In my improved relay I have utilized, for this purpose, anelement somewhat analogous to the grid used in the ordinary thermionic tube.

Referring specifically to Fig. 1 my discharge device comprises a glass envelope l having mounted therein a press 2 from which are supported a cylindrical cathode 3 and a central anode 4. The central anode t is surrounded by a glass tube 5 which is either continuous with or is welded to, the material of the press 2. A metallic screen 45 element 6 encircles the glass tube and fits closely. over the exposed upper end of the anode 5. Suitable conducting leads l, 8 and 9 extend from the various electrodes to the exterior of the tube and are connected to a plurality of contact posts I0, 50 l l and I2 carried by a base element l3, into which the tube is cemented.

The cylindrical cathode 3 may be made of substantially any metal, although I have preferably employed nickel for this purpose. The grid or screen 6 and the anode are also preferably made of nickel.

It is very important that the grid be placed quite close to the exposed end of the wire, a space of therebetween being amply sufiicient.

In the manufacture of the device, the glass envelope carrying the various electrodes is first carefully exhausted while being heated at a temperature of 460 C. The preliminary exhaust should last for at least an hour in order to make sure that all occluded gas and water vapor are driven out of the electrodes.

A small amount of argon or neon is then admitted into the tube, sufficient being used to raise the pressure therein to approximately two millimeters mercury. fair results, though I prefer argon or neon.

Before removing the tube from the source of gas, an alternating potential of approximately 440 v. is applied between the anode and the cathode, and the gas pressure is adjusted until a glow discharge occurs between these electrodes at a predetermined potential. The tube is then sealed off and may be supplied with a base, as indicated in the drawing, if desirable.

In operation, a source l4 of alternating potential is applied between the anode 4 and the cathode 3. If the grid element 6 is grounded, the gas in the tube will ionize and conduct current at a definite potential, in the same manner as in glow tubes of the usual type. The current is mainly from the wire anode to the cylindrical cathode, the percentage of inverse current being very small.

If the grid is now insulated from ground as shown in Fig. l, electrons will be accumulated thereby during such times as the electrode 4 is positive. When the polarity changes so that the electrode 4 is negative and the electrode 3 is positive, the previously accumulated charge on the grid remains, and each successive reversal in polarity serves to increase it. This negative charge on the grid lowers the effective gradient between the grid and the electrode 3 to a value insuflicient to cause ionization and increases the gradient between the grid and the electrode 4. The distance between the grid and the electrode 4, however, is quite small as compared to the distance between molecules of the gas, so that a glow discharge does not occur between the said electrodes. The insulating property of gases between closely spaced electrodes is quite well known in the art and is styled the short path principle. It is based on the fact that a gas between electrodes will not ionize if the electrodes are spaced apart by a distance no greater than the mean free path of a molecule of the gas. It is thus apparent that, with the proper alternating potential source I4 impressed between the electrodes 4 and 3 and with the grid floating, only a very small current will flow when the central electrode is the cathode, and substantially no current will flow when the central electrode is the anode.

If, however, the grid is grounded in order to prevent a charge being accumulated thereon or to conduct away a previously accumulated charge, this grid-efiect is lost, no charge being present to prevent a current flow when the cylindrical element becomes the cathode. The result is that a rectified alternating current flows in the same manner as in any well known point-to-plane rectifier.

When charged, the grid potential is extremely high, making it possible to remove the charge I have utilized helium withthrough a resistance of a megohm or more to ground. In certain instances, it is not even necessary to connect the grid to ground in order to remove the charge, contact with the body, or with any object I6 having an appreciable capacity, being sufficient to lower the potential to the point at which the discharge starts.

The sensitivity of the device to the grid charge may be varied by varying the operating voltage on the tube. If the voltage is raised, the grid will charge to a higher potential and the tube becomes more sensitive. With lower voltage, a better contact with ground is necessary to remove the charge, in order to render the tube conductive.

The device is practically self-adjusting. If the grid is left free and unconnected to ground, or to a capacity area, it will of itself, assume a charge sufficient to block the main discharge in the tube.

The output of rectified current when the tube is energized from an alternating current source may be as high as 100 milliamperes at 100 volts. This current is amply sufficient to energize a tenwatt incandescent lamp connected directly in circuit with the discharge device.

My relay device is useful in a variety of applications. As a burglar-alarm-controlling device, an arrangement could be made in which a door knob would be insulated from ground and connected to the grid, or the grid could be connected to any other object which an intruder would be likely to handle. Upon touching the protected object, the grid charge would immediately be dissipated'and the output current of the device could then be utilized toeither ring a bell or actuate an indicating device i 8 of some other type.

The device would also be useful in connection with recording meters and the like, where a pointer, incapable of carrying a heavy current, could be utilized to carry off the grid charge.

It is also feasible to control the leakage of the grid charge by means of a photo-electric cell 20, as shown in Fig. 2, thus giving an indication when the light reaches a certain predetermined condition.

The photo cell could obviously be extremely small and inexpensive, inasmuch asit would merely be utilized to vary the conductivity of a leakage path for the grid charge.

In the claims, the expression photo-electric tube is used. This expression I intend to be taken as synonymous with photo-electric cell. In using the expression in the claims, I intend to limit myself to a light-sensitive cell of the type that operates by reason of emission of electrons from the surface of a body on which light impinges, to produce a space discharge in the region of the body. A photo-electric cell also includes a collecting electrode disposed in the region of the emissive body but not in contact therewith. If a potential difference is impressed between the collecting electrode and the body, the charge from the body flows to the collecting electrode.

By the expression unexcited cathode I mean a cathode that is not, in the normal operation of the apparatus, excited by an external energy source to emit electrons.

Although I have illustrated and described a specific embodiment of my invention, obvious modifications will be apparent to those skilled in the art. My invention, therefore, is not to be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination, a device comprising an evacuated envelope containing a cathode, a normally completely insulated electrostatic control member, an anode and an inert gas at a pressure sufficient to support an arc-like discharge at the impressed voltage, a source of alternating current for impressing potentials between said anode and cathode, a load circuit connected between said anode and cathode and means including a photoelectric cell for connecting said electrostatic control member in such manner that the charge accumulated thereon may leak off to energize said 1 device.

DEWEY D. KNOWLES. 

